The present invention pertains to portable power supplies having removable and replaceable electrochemical cells. In particular, the invention pertains to power supplies employing multiple replaceable primary or secondary cells.
New portable electronic devices, such as laptop computers, need thinner, lighter batteries delivering more power and energy capacity. A thinner shape is needed to fit in the smaller and smaller forms of these electronic devices. Capacity demands require a large total battery volume, with the result being a drive toward large thin battery packs. However, a large thin battery is highly susceptible to damage through twisting, bending or folding. When battery packs are inserted or removed from a powered device or handled by a user, they become exposed to these kinds of actions. This is potentially dangerous as it can cause internal shorting of the cells. Battery packs having aspect ratios in excess of 50:1 (maximum edge-to-edge planar dimension to thickness) are particularly susceptible to damage. The dangers are of particular concern with the cells most desired to be used for thin high capacity battery packs, such as, for example, lithium ion polymer cells. Due to the chemical composition and operating characteristics of these cells, events such as shorting can result in fires. Current lithium ion batteries of any configuration incorporate protective circuit elements physically attached to the individual battery packs to protect against operation during extreme voltage, current or temperature conditions. The need for these additional elements on each pack add to the complexity and cost of the packs. An additional protection method is to provide a key or concealed switch on the battery pack which must be activated to connect the battery pack terminals to the enclosed cell. In this way, inadvertent contact with the terminals by the user will not result in shorting of the cell. Mechanical locks have been used in prior battery packs but are typically too easily circumvented, allowing the user to place themselves at risk.
One part of the solution to the risks in large thin battery packs is to subdivide the battery into smaller modularized packs, each less susceptible to damage. However, the need to include protective devices on the individual packs results in significantly increased cost and weight of the pack. Additional parts also increase the risk to the user in handling.
What is needed is a simple and secure method of modularizing thin cells to form a large thin battery pack.
The present invention provides a modularized power supply using multiple cell modules that are rendered electrically inert until activated when combined with an external circuit having specific response characteristics. Each cell module is separable from the power supply and includes at least one primary or rechargeable secondary cell. In each module, at least one of each cell""s terminals is isolated from the exposed contacts of the cell module when the cell module is separated from the power supply, reducing the opportunity for improper charge or discharge of the cell. The cell terminals are isolated by a disabling circuit packaged with the cell in the cell module. The disabling circuit includes a switch and switch control which are activated when the disabling circuit is connected to an external unlocking circuit having defined characteristics. When activated, the switch connects the cell terminals to the exposed cell module contacts, allowing access to the stored cell energy or for charging functions. The characteristics of the external unlocking circuit are defined by the disabling circuit and must generate a specific response in the disabling circuit which activates the switch control and switch. This event is a result of the unlocking circuit being energized solely by the cell energy. This is because it is presumed that the cell module will be connected with an otherwise unpowered host device. In effect, the cell module remains inert until xe2x80x9cself-awakeningxe2x80x9d when connected to an appropriate (otherwise unpowered) external circuit.
Because a host device most likely requires power of a specific characteristic such as voltage, it is necessary to ensure that the individual cell modules are not connected to the host until a full complement of modules have been successfully connected to provide the characteristic power. An enabling circuit is provided on a frame to which cell modules are physically connected. The enabling circuit includes the unlocking circuits for each connected module and includes logic circuitry which enables the cell modules to be connected to a host only when a full complement of cells are connected. The enabling circuit and disabling circuit may also include devices for passing and receiving identification signals between the frame and the cell modules. The identification signals allow validation of appropriate cell modules prior to enablement with the specific power supply.
The frame may also include a control circuit providing cell protective elements, charging circuits and cell monitoring circuits. Because the individual modules are otherwise rendered inert, a single set of protective devices for all of the cell modules can be provided in the frame. Similarly, cell charging and discharging control circuits and cell monitoring circuits may be included in the control circuit. The number of modules combined in one battery pack is dependent upon the power requirements of the host device to be powered and the capacity of the individual cells. The number of modules may be from two to twenty although the concept of the xe2x80x9cself-awakeningxe2x80x9d cell module is applicable to a single cell power supply.
An additional advantage of multiple modularized cells is increased design flexibility as various combinations of a single module configuration may be joined to satisfy different performance requirements. In various embodiments, the frame may be integral with a host device or is an independent structure such as a tray. When the power supply is integrated into a host device, the enabling circuitry and control circuitry may be alternatively integrated with existing host electronics. An independent tray including modules is configured as a battery pack removable from host device interface contacts and replaceable as a unit. The frame has receptacles such as open-sided pockets or slots for receiving the modules and includes a module interface having contacts associated with each receptacle. Using cell designs that can be configured to form cell modules that are small and thin, but having maximum aspect ratios preferably less than 50:1, flat large capacity power supplies and battery packs with high aspect ratios are formed. The relatively small size and aspect ratio of the modules, as compared to an equivalent single flat cell assembly, results in a more durable unit for user handling. Combined with described cell module""s inertness during handling, the modularization of the energy capacity into a multiple of modules provides a uniquely strong and secure replaceable power supply. Other advantages of the present concepts will become clear from the following detailed description and figures.